A.S. Korhonen

Improved corrosion resistance of physical vapour deposition coated TiN and ZrN

Abstract TiN and ZrN coatings were deposited by reactive triode ion plating onto high-speed steel rods, and onto both rods and strips of austenitic stainless steel. Various methods were studied in order to improve the corrosion resistance of these coatings. They included the pulsing of nitrogen flow, the rotation of the specimen and separate sputtering during deposition. Different post-deposition methods were also studied. They included chemical passivation and annealing in vacuum. Corrosion tests were used to study the effectiveness of these methods. Cross-sectional scanning electron microscopy and Auger analysis were used to study the structure and morphology of the coatings. It was found that all of the methods studied improved the corrosion resistance of TiN and ZrN coatings.

Comparison of cutting performance of ion-plated NbN, ZrN, TiN and (Ti, Al)N coatings

Abstract Three binary nitrides of the refractory materials titanium, zirconium and niobium and ternary (Ti, Al)N as well as quaternary (Ti, Al, V)N coatings were deposited by reactive triode ion plating on powder metallurgically produced high-speed steel (PM-HSS) inserts. The coated tools were then tested by dry turning of hardened and tempered AISI 4140 steel. The effect of the deposition parameters on coating properties was studied in detail. The results showed that NbN coating does not seem to improve the wear resistance in the turning of steel. Titanium-based nitride films such as TiN and (Ti, Al)N, however, appeared very suitable, as they showed increasing cutting performance and finer structures with increasing substrate current density. ZrN, however, showed the opposite effect. The best turning properties were achieved with a substrate bias of −100 V. Increasing thickness improved cutting performance almost linearly in the range from 1 to 5 μm. Substrate polishing before the deposition of the TiN layer had a strong effect, almost corresponding to doubling of the coating thickness. For example, a thickness increase from 3 to 5 μm yielded a performance improvement which could also be achieved simply by polishing the substrates carefully before coating. The three best coating materials in decreasing order of performance were ZrN, (Ti, Al)N and TiN. The differences between the best coating materials were generally not large.

Ti–N phases formed by reactive ion plating

Thin Ti–N films were prepared by reactive triode ion plating. The nitrogen content was varied from 17 to 50 at. % nitrogen. Two series of experiments corresponding to differing values of deposition rate and cathode current density were carried out. The nitrogen depth profiles were analyzed using the nuclear resonance broadening (NRB) technique. The performance of the coatings was evaluated in cutting tests. The films corresponding to a high deposition rate showed columnar growth morphology and consisted of metastable α‐titanium and cubic titanium nitride. Dense and noncolumnar films approaching the structures predicted on the basis of the bulk phase diagram could be produced with a lower deposition rate and higher current density. The best cutting performance was obtained with substoichiometric films containing about 36 to 42 at. % N and consisting of a Ti+Ti2N structure. The lifetimes corresponding to critical crater wear in turning increased ninefold after coating with substoichiometric Ti+Ti2N film, wh...

Comparison of the corrosion resistance of TiN and (Ti,Al)N coatings

Abstract The corrosion resistance of various commercially available TiN-based physically vapor deposited coatings were compared. All coatings were deposited onto stainless steel substrates. The corrosion resistance of the samples was studied using anodic polarization and potentiostatic measurements. The film structure and substrate-coating interface chemistry were studied using X-ray diffraction, scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS). All samples had good corrosion resistance under short-term anodic polarization measurements but clear differences could be observed in the long-term potentiostatic experiments. The corrosion resistance was found to be based on two factors: (i) the degree of porosity in the thin film and (ii) the nature of the coating-substrate interface. The proper chemistry of the coating-substrate interface appeared to be important in achieving good corrosion resistance. TiN samples with proper chromium and chromium oxide distribution at the substrate-coating interface together with one (Ti,Al)N coating chosen for the study showed the best corrosion performance.

Plasma nitriding and ion plating with an intensified glow discharge

Abstract Ion plating and plasma nitriding at low pressures with a glow discharge supported by a hot electron-emitting filament are studied. The properties and applications of titanium nitride coatings are discussed. Examples of their use for wear reduction in cutting are presented and their frictional properties are investigated. The triode technique is also applied in plasma nitriding and the effects on nitrogen penetration are discussed. In a steel with low contents of carbon and chromium considerable increase in the thickness of the diffusion zone is obtained by using the triode system. Further, it is shown that plasma nitriding can be combined with subsequent ion plating in order to prevent abrasive wear.

The role of neural networks in the optimisation of rolling processes

Abstract Applications of neural networks in the rolling of steel are reviewed. The first papers on the topic were published in 1991 and since then the number of publications has steadily increased. In most applications today, so-called back propagation networks are used. After briefly reviewing the various neural network types, the results of two case studies at Rautaruukki cold strip mill are presented. In the first case an efficiency model for tandem cold rolling was developed. By using the model it is possible to study whether a new product with a given width, strength or thickness can be produced, and the optimised mill settings can then be determined. A 1.8% improvement in efficiency was obtained with the model. The second case concerns the prediction of the mechanical properties of steel strips and temper rolling force by using neural network modelling and measured process data. The location of the coils in annealing stacks and their vanadium content were found to explain the deviation in mechanical properties. The temper rolling force could be predicted with good accuracy, which can be exploited in determining mill pre-settings.

A study of nitrogen‐rich titanium and zirconium nitride films

Thin titanium nitride (TiN) and zirconium nitride (ZrN) films containing excess nitrogen up to 59 and 63 at. % N, respectively, were deposited on austenitic stainless‐steel substrates by reactive triode ion plating at about 823 K. The film structure and surface chemistry were studied using x‐ray diffraction, scanning Auger spectroscopy, and electron energy‐loss spectroscopy (EELS). In TiN films only the face‐centered‐cubic mononitride phase was detected. The lattice parameter of the stoichiometric TiN film was larger than the corresponding bulk value and it increased with increasing nitrogen content. The lattice parameter of overstoichiometric ZrN films showed abnormal behavior when calculated from different diffracting planes. This behavior together with the EELS and other measurements indicate that a dielectric Zr3N4 phase was formed at overstoichiometric compositions.

Strategic financial management in a multinational financial conglomerate: A multiple goal stochastic programming approach

Abstract The paper discusses a multi-stage stochastic programming approach to the strategic financial management of a multi-company financial conglomerate. The planning system creates a comprehensive strategy which simultaneously covers a number of future scenarios within a multi-period planning horizon. Multiple conflicting goals may be specified for the group level, company level or individual business area level, and the decision maker’s preferences are allowed to change over time to reflect changing operating conditions and trade-off relationships between the goals. Special features include, among other things, full market valuation throughout the model, integrated treatment of different types of risks, explicit modelling of various types of intra-group transactions and relationships, extensive structures to deal with distressed assets and the covering of losses within the group, as well as consideration of potential portfolio effects of a diversified group structure on the cost of funding.

Prediction of rolling force in cold rolling by using physical models and neural computing

Abstract In this study physical models and a neural network theory have been integrated to a program package in order to predict rolling force in cold rolling. The parameters required by the model such as the friction parameter and the deformation resistance of the materials have been determined from measured rolling parameters and materials alloying elements by applying the Bland-Ford-Ellis (BFE) rolling force model and an artificial neural network model (ANN). Measured data of over 6000 coils have been used in the training of the ANN. The calculated results were in good agreement with measurements.

A dynamic bank portfolio planning model with multiple scenarios, multiple goals and changing priorities

Abstract The paper discusses a practical application of a two-stage linear goal programming model to the management of the domestic and foreign currency denominated assets and liabilities of a large bank in Finland. The planning horizon includes three one-year planning periods. A number of alternative scenarios are used to describe uncertainty concerning future developments in these periods. The scenarios are related to general economic conditions as well as the state of the domestic and foreign financial markets. The bank is assumed to have multiple conflicting goals with different and changing priorities. The goals deal with expected profits, risk, liquidity, capital adequacy, growth, customer relationships and several other aspects of the banks operations.